GMS, I have been going through the same thing for a while to be honest and it's made me think about stopping drinking again too. Only in my mid 30s but don't feel my brain is where it 'could or should' be. I'm often quite forgetful. The thing for me is that (I suppose I am bargaining here) I wonder, as a 'moderate' drinker, whether its the alcohol that is effecting me, or other things in my lifestyle. In reality it is hard to pinpoint the exact issue.
Having said that, alcohol would be an obvious place to start, I guess.
I've been sick on and off now since mid September.